How to display background images in perspective?
Background images will only be displayed in


  Camera Prespective view (Numpad 0)


Any of the Preset Orthographic views


  
  Front/Back (Numpad 1 or CtrlNumpad 1)
  Right /Left (Numpad 3 or CtrlNumpad 3)
  Top/Bottom (Numpad 7 or CtrlNumpad 7)
  


Background images will not show in perspective view. 

To switch between Perspective and Orthographic view use Numpad 5

Background images are used for reference only and will not be part of the final render.



Alternatives to background images are to use an empty as image or using a plane with the image mapped to it.

To use an empty as image use Add> Empty >Image



Select the image in the properties->Empty->Display tab



Alternatively, you can use the image as background for the world. Set the Texture coordinates to Window.